Voice over internet protocol (VOIP) has become popular and prevalent for communications. VOIP systems may use different protocols, such as H.323 and session initiation protocol (SIP), to set up calls. Previously, end devices communicating using different protocols, such as one end device communicating an H.323 and another end point communicating using SIP, could not communicate. However, basic connections for interworking the H.323 and SIP protocols has been addressed where a call between two parties can be set up when the H.323 and SIP protocols are being used. However, the interworking defined includes only basic connections and does not provide interworking for supplementary features that are either provided by H.323 or SIP.